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What is DMARC?

Domain-based Message Authentication Reporting & Conformance (DMARC) is an email security protocol. DMARC verifies email senders by building on the Domain Name System (DNS), DomainKeys Identified Mail (DKIM), and Sender Policy Framework (SPF) protocols. 

The DMARC standard was created to block the threat of domain spoofing, which involves attackers using an organization’s domain to impersonate its employees. It also supplements Simple Mail Transfer Protocol (SMTP), which is the basic protocol used to send email messages, but does not include mechanisms for defining or implementing email authentication.

How Does DMARC Work?

DMARC requires DKIM or SPF to be in place on an email domain and a DMARC record to be published in the DNS. The DMARC policy process, also known as DMARC alignment and identifier alignment, enables the email domain’s policy to be shared and authenticated after the DKIM and SPF status has been checked.

An SPF DKIM DMARC record requests email servers to send Extensible Markup Language (XML) reports to the email address associated with the record. A DMARC checker report provides information about how email moves through a system and enables users to identify all traffic that uses their email domain.

Why Use DMARC for Email?

A DMARC record enables domain owners to protect their domains from unauthorized access and usage. This is crucial as email is increasingly vulnerable to cyberattacks, such as phishing, spoofing, whaling, chief executive officer (CEO) fraud, and business email compromise (BEC).

Furthermore, email-based attacks have resulted in people losing trust in email despite it continuing to be one of the most-used communication forms. DKIM and SPF have been used to identify and validate senders for years but did not allow flexibility over what happened if the sender was invalid. This prevented domain owners from taking complete control of their brand, hence the need for DMARC email security.

What Are the Benefits of DMARC?

DMARC authentication helps domain owners prevent domain spoofing. It is necessary for all United States government agencies and contractors, while other countries have mandated its use by all public bodies and institutions. 

The benefits of DMARC include:

Reputation

When a domain owner publishes a DMARC record, it protects their brand by preventing unauthorized users or third parties from sending emails from their domain. The process of publishing a DMARC record can, in some cases, give an organization an immediate boost in reputation.

安全性

DMARC provides a consistent policy for email domain owners to handle messages that are not validated or authenticated. As a result, the entire email ecosystem is inherently more secure and trustworthy.

可見度

A DMARC report increases the visibility of domain owners’ email programs. This ensures they know who is sending email messages from their domain.

What Is a DMARC Record?

A DMARC record is included within an organization or domain owner’s DNS database and is a specific version of DNS text records (TXT records). The full DMARC record looks similar to this: “v=DMARC1\; p=none\; rua=mailto:dmarc-aggregate@mydomain.com\; ruf=mailto:dmarc-afrf@mydomain.com\; pct=100”. These various sections within the DMARC record signify:

  1. v=DMARC1: The DMARC version specified.
  2. p=none: The domain owner’s DMARC policy or preferred treatment of any email messages.
  3. rua=mailto:dmarc-aggregate@mydomain.com: The email address to which aggregate reports need to be sent. 
  4. ruf=mailto:dmarc-afrf@mydomain.com: The email address to which forensic reports need to be sent.
  5. pct=100: The percentage of email that needs to be subjected to a DMARC policy’s specifications. In this case, 100% of email messages that fail a DMARC test will be rejected by the server.

What Is DMARC Domain Alignment?

Domain alignment is a DMARC concept that matches the domain of an email against SPF and DKIM. A DMARC record can have varied strictness of DKIM alignment, which affects whether messages will be allowed to pass through the DKIM process. The alignment can either be relaxed, which matches base domains but allows different subdomains, or strict, which precisely matches the whole domain

What Are DMARC p=Policies?

The policy a domain owner uses in their DMARC record tells the receiving email server what it should do with email that fails DKIM and SPF checks but claims to be from a domain. There are three policies, which are signified by ‘p= policies,’ available:

Signified by ‘p=none,’ this advises the receiving server to perform no action when receiving an unqualified email. However, the server will send email reports to the email address in the DMARC record.

Quarantine

Signified by ‘p=quarantine,’ this advises the receiving server to quarantine any unqualified email. As a result, emails will typically reach recipients’ spam folders.

拒絕

Signified by 'p=reject,' this advises the receiver to deny unqualified email messages. It ensures only email messages that are 100% verified as being from a domain will reach inboxes. Any email that fails checks will be denied. 

What Is a DMARC Report?

The DMARC validation process sees inbound mail servers generate DMARC reports. These come in two formats, which are both included within DMARC records and precede an email address to which the report needs to be sent.

Aggregate Reports

Aggregate reports are XML documents that provide statistical data about email messages that claim to be from an email domain. They include data like authentication results and message disposition and are machine-readable only. Aggregate reports are signified by ‘rua=mailto’ in the domain record and can be sent to any email address.

Forensic Reports

Forensic reports are copies of email messages that have failed authentication. They help troubleshoot a domain’s authentication issues and identify malicious websites and domains. Forensic reports are signified by ‘ruf=mailto’ in the domain record and can only be sent to the email domain the DMARC record was created for.

How Is DMARC Related to SPF, DKIM, or Other Standards?

DMARC, DKIM, and SPF are all standards relating to different areas of email authentication. SPF enables senders to define the Internet Protocol (IP) addresses that are allowed to send email from their domain. DKIM verifies email messages using a digital signature and an encryption key, ensuring email messages cannot be altered or faked. 

DMARC unifies these two standards into a common framework. It enables domain owners to advise how they want email from their domain to be handled if it fails authorization.

Implement DMARC with Fortinet

Fortinet protects email domain owners and users with FortiMail, a comprehensive secure email gateway solution. FortiMail is designed to detect and prevent inbound and outbound threats and works seamlessly with popular email services, such as Exchange, Microsoft 365, and Google Workspace. The solution can detect malware, such as ransomware and viruses, and includes techniques that prevent targeted attacks and stop users from downloading risky files.

The FortiMail solution is supported by FortiGuard Labs, which has visibility into more than 100 million unique emails and offers intelligence into real-time threats. This protects organizations from the latest spam, malware, and virus outbreaks as quickly as possible. 

Discover how to enable Fortinet DMARC, DKIM, and SPF in FortiMail.